lecture 1

Question 1

what are the functions of the stomach?

Answer 1

• store and liquefy food
• liquefaction (acid, pepsin, muscle contractions)

Question 2

what is the anatomy of the stomach?

Answer 2

• oesophagus (enters top)
• sphincter (
• greater and lesser curvature (corpus)
• antrum (bottom part)
• pylorus (better sphincter)

Question 3

what does the sphincter do?

Answer 3

• controls movement of fluid
• air escapes through forming burp

Question 4

what is the function of pylorus?

Answer 4

• allows fluid/material to empty out into duodenum
• better sphincter than cardiac sphincter

Question 5

what happens to musculature from top to bottom?

Answer 5

• increases
• more muscular in antrum

Question 6

what are the layers of stomach wall?

Answer 6

• outside = connective tissue, muscle, autonomic nerve plexus
• middle = submucosa (lots of blood supply)
• inner = gastric glands, epithelium, lymph nodes

Question 7

when are goblet cells found in the stomach?

Answer 7

• if pre cancerous changes occur (only found when in diseased state)

Question 8

what is the structure of the gastric gland?

Answer 8

• top = mucus secreting neck cells
• middle = stem cells, parietal and chief cells
• bottom (base) = neuroendocrine cells

Question 9

where are gastric glands found?

Answer 9

• gastric pits

Question 10

what do mucus secreting neck cells migrate to form?

Answer 10

• epithelium of surface of stomach
• secrete mucous

Question 11

what are neuroendocrine cells?

Answer 11

• are nerve cells that make hormones

Question 12

what neuroendocrine cells are present in base of glands?

Answer 12

• enterochromaffin
• enterochromaffin like cells
• D cells
  (change function based on location in gland)

Question 13

what do enterochromaffin cells secrete?

Answer 13

• serotonin

Question 14

what do enterochromaffin like cells (ECL) secrete?

Answer 14

• histamine (control of acid secretion)

Question 15

what do D cells produce?

Answer 15

• somatostatin

Question 16

what do G cells secrete?

Answer 16

• gastrin (control of acid secretion)

Question 17

where is acid secretion happening?

Answer 17

• top of stomach
• antrum doesnt secrete
• pepsinogen secreted all over

Question 18

what do surface epithelial cells secrete?

Answer 18

• mucus
• forms continuous mucus layer
• first line of defence against gastric juice

Question 19

does the continuous layer of mucus extend into oesophagus?

Answer 19

• no
• stomach has columnar epithelium
• oesophagus is squamous epithelium (dead cells at surface so no need to protect- don’t need layer over dead cells) - doesn’t have a mucus layer

Question 20

what is the structure of gastric mucus bilayer?

Answer 20

• 2 layers within the mucus layer
  (protection for stomach)

Question 21

what are the two layers?

Answer 21

• shear compliant layer
• shear resistant layer

Question 22

what is the shear compliant layer (on top)?

Answer 22

• gel but can be converted to viscous liquid
• becomes lubricant
• has variable thickness

Question 23

what is the shear resistant layer?

Answer 23

• remains intact
• 150 um thick

Question 24

what is the purpose of the layers?

Answer 24

• opposes the degradation from pepsin

Question 25

how is the layer maintained?

Answer 25

• secreted from epithelial cells underneath the layer
• secretion balances degradation to maintain the layers (dynamic balance)

Question 26

what is the composition of gastric juice?

Answer 26

• mucus (salary and gastric)
• lipases
• pepsins
• urea
• intrinsic factor and haptocorrin
• H20
• ions
• salivary amylase

Question 27

what is the purpose of the mucus in gastric juice?

Answer 27

• lubricant so food can pass down oesophagus

Question 28

what is the purpose of the lipase in gastric juice?

Answer 28

• aids in fat digestion

Question 29

what is the function of salivary acid in the gastric juice?

Answer 29

• not active
• gastric juice shouldn’t be pH7 which is optimal for amylase

Question 30

what is gastric lipase pH activity?

Answer 30

• between pH 2.5 and around 5-6

Question 31

how does pH change?

Answer 31

• food buffers gastric juice
• allows pH to increase to around 5

Question 32

how does acid secretion occur?

Answer 32

• when stimulated (by histamine and gastrin), H2 receptors bind
• hydrogen potassium pumps trafficked to membrane when stimulus present (require ATP)
• tubulo cysterni migrate along actin cytoskeleton to membrane (supported by actin scaffold)
• secrete acid

Question 33

what is the tubulo cysterni?

Answer 33

• series of plates where pumps are stored

Question 34

what happens once stimulus its removed?

Answer 34

• dissolving of actin scaffold
• pumps travel back to tubulo cysterni

Question 35

what is the treatment for gastric ulcers?

Answer 35

• H2 antagonists (stops the acid secretion)
• proton pump inhibitors (PPIs)

Question 36

what is the function of carbonic anhydrase?

Answer 36

• forms bicarbonate that dissociates into hydrogen ions and co2

Question 37

what happens to the dissociated bicarbonate?

Answer 37

• transferred out across basolateral membrane
• chloride enters
• hydrogen pumped out
• hydrochloric acid forms

Question 38

how is the HCl produced?

Answer 38

• chloride channel present
• exchange of hydrogen ions for potassium (brings potassium in)
• potassium channel to allow exit

Question 38

what is the H+/K+ATPase?

Answer 38

• intracellularly = app activator, catalytic site
• lots of transmembrane sections (needs conformational changes)
• mostly alpha subunit, 1 beta

Question 39

how does the ATPase bind with PPI?

Answer 39

• forms disulphide bridge with present cystine

Question 40

what happens when you stop taking PPIs?

Answer 40

• surge of acid secretion
• need maintenance dose